Recording and reproducing sound



April 15, 1941. E. w. HULLEGARD 2,238,735v

RECORDING 'AND REPRODUCING SOUND Original Filed March 17, 1958 2 Sheets -Sheet l April 1941- E. w.' HULLEGARD 2,238,735

RECORDING AND REPRODUCING SOUND Original Filed March 17, 1958 2 Sheets-Sheet 2 3nventor Patented Apr. 15, 1941 RECORDING AND BEPRODUCING SOUND Erik Waldemar Hullegard, Stockholm, Sweden,

assignor, by mesne assignments, to Radio Corporation of America, a corporation of Delaware Original application March 17, 1938, Serial No. 196,554. Divided and this application October 17, 1940, Serial No. 361,573. In Sweden March The present invention relates to such systems for recording and reproducing sound through the intermedium of light-sensitive media, such as photographic films and photocells, in which the positive and negative half-waves: of the sound oscillation curve are recorded on the light-sensitive medium independent of one another to facilitate their separation in the reproduction through the intermedium of the photocells.

This application is a division of my application Serial No. 196,554, filed March 17,1938.

The advantage is afforded that no biasing illumination of the light-sensitive medium is required on which illumination the sound oscillations are optically superposed so that the background will be much more silent than in previous systems having a biasing illumination. In a known system, the positive and negative halfwaves of the sound curve are recorded each in one of two coextensive tracks which necessitate the provision of complicated apparatus having means for the simultaneous reproduction of two tracks. These two tracks require further a space of th light-sensitive medium, such as a film, which is double that of an ordinary single track.

According to the present invention, said inconvenience is eliminated by arranging that the positive and negative half-waves of the sound curve are not recorded in positions transversely displaced in relation to one another but in one and the same track while receiving such distinctive properties that the record of each halfwave could be separately reproduced. In case the film is color-sensitive, the positive and negative half-waves of the sound curve could be converted each to a light bundle of a distinctive color,

to which the filmis exposed.

The invention will now be more fully described with reference to the accompanying drawings illustrating, by way of example, two embodiments of the invention. On the drawings,

Figure l is a perspective and diagrammatic view of a preferred embodiment of a recording device, whereas Figure 2 is a circuit diagram of areproduction device,

Figure 3 is a similar diagram of a recorder adapted to produce a variable density record, and

Figure 4 illustrates a modified type of reproducer in which the two photoelectric elements are arranged with a single anode within the same container.

In Fig. I, condensing lenses L1 and L2 and a diaphragm S1 are positioned in a straight line be tween a source of light I and an oscillating mirror 1 Claim. (Cl. ire-400.3)

2, as shown in Fig. 1. The diaphragm S1 consists triangular transparent fields, i. e., 4, 5 on the leftof an opaque or nontransparent portion 3 and four hand side of the diaphragm and 6 and 'I on the right-hand side of the diaphragm. The fields 4 and 5 have one distinctive color and fields 6 and 1 another distinctive color. The triangular fields turn their points towards one another, as shown, while leaving an opaque zone between opposing points.

Further condensing lenses L3 and L4 and a slit device S2 are positioned in a straight line between the oscillating mirror 2 and a light-sensitive band 8 in such an angular relationship to the path between parts I and 2, in an averageposition-of the mirror 2, an image of the diaphragm S1 is projectedon the slit device S2. The sharp-edged slit 9 provided therein has a width corresponding to the opaque zone between opposing points in the diaphragm S1 so that, in the mentioned position of the mirror, the image of the opaque zone covers the slit 9 and no light can penetrate to the color-sensitive film 8.

The mirror 2 is connected to an oscillograph responsive to the sound to be recorded and which is not shown on the drawings.

When the mirror 2 starts oscillation, the image of the diaphragm S1 oscillates to and from over the device S2 so that the translucent portions 4 and 5 alternating with the portions 5, I send light of corresponding color through the slit 9 on to the film 8. The transversal width or, in this instance, the vertical extension of the bundle of rays reaching the film will apparently depend on the vertical dimension of the translucent portions 4 to I projected on to the slit device and thus on the angular deflection of the mirror 2 or the amplitude of the sound wave corresponding thereto. Provided the film band 8 is moving at a sufiicient rate crosswise to the slit 9, there will accordingly be recorded impressions which, when the film is developed, will appear as oblong traces in, II of the one or the other color on an opaque background 24, depending upon the translucent portions 4, 5 or 6, I which is operative at the moment,

In Fig. 2 is shown a reproduction device consisting of a light source l2, condensing lenses L5 and Le, stationary mirrors l3, I4, put at an angle to one another, color filters S3 and S4, each letting through only light corresponding to the one color of the translucent portions 4, 5 or 6, I, respectively, and photocells P1 and P2. These latter are associated in push-pull connection with an amplifier A and a loudspeaker B.

In the shown embodiment, there are two pairs of opposing translucent filter portions 4, 6, and 5,

1, respectively. Instead thereof, only one pair. of

section passes only blue light, a variable density record is produced. This necessarily follows from the fact that, when the mirror 2 is at rest, no light is passed through the slit 9, and, when the light beam is vibrated transversely of the slit, a red penumbra shadow is produced for one direction of the vibration, and a blue penumbra. shadow is produced for the opposite direction of vibration. In this record, the alternate half several pairs of opposing translucent portions can used. The points of such portions need not be positioned exactly opposite one another, reckoned in a plane parallel with. the path of movement of the film band, but may be staggered, in which case the traces on the film band'will be correspondingly staggered, although grouped symmetrically in regard to an imaginary base line on the film which line is parallel with the path of movement of the film.

The two photocells shown in Fig. 2 could be combined, as shown in Fig. 4, to a single one having, for instance, two cathodes l1 and I8 and one anode l9. In this arrangement, the lenses I5 and I6 perform the same function as the reflectors l3 and M of Fig, 2.

Whereas the above-described apparatus refers to such sound films which are modulated according to the amplitude method, the invention could likewise be applied to sound films, based on an intensity-modulation, and in systems using a combination of amplitudeand intensity-modulation.

Thus, if the aperture plate S1 be modified so that its center section 3 is opaque, its left-hand section 4 passes only red light, and its right-hand cycles 20 and 2| are of difierent colors, as indicated in the drawing. This type of record may evidently be reproduced by any reproducer involving a color-selecting prism or other device suitable for causing light modulated by alternate half cycles to be applied respectively to the cathodes l'! and I8. The reproducer of Fig. 4 is suitable for this purpose. This reproducer is also capable of reproducing either of the two tracks of the record of Fig.1.

The foregoing method and apparatus are particularly useful with the present type of color films wherein a plurality of color-sensitive layers are provided and the exposure and development produce appropriate colors in each of these layers, as distinguished from earlier types of color films in which each color was printed separately on to the positive.

Having now described my invention, I claim:

In a sound-recording apparatus of the galvanometer-operated variable area type, an aperture plate having an opaque portion defining a pair of oppositely directed light transmitting triangular portions having oppositely located vertices pointed towards one another, and difierently colored filter means interposed in said light-transmitter portions.

ERIK WALDEMAR HULLEGARD. 

